# _manifest.json

> 91 lines of code and 0 definitions.

Tree: Content Fingerprint
Language: json
Canonical: https://banes-lab.com/anatomy/content-fingerprint#file-content-fingerprint-manifest-json
Source text: https://banes-lab.com/source/content-fingerprint/_manifest.json.txt

Listed in [Content Fingerprint](https://banes-lab.com/api/source/content-fingerprint.md), after [types](https://banes-lab.com/api/source/content-fingerprint/types.md) and before [index.ts](https://banes-lab.com/source/content-fingerprint/index.ts.md).

## Contained in

- [root](https://banes-lab.com/anatomy/content-fingerprint/folder-content-fingerprint.md)

## Source

```json
{
    "label": "Content Fingerprint",
    "summary": "Deterministic content-hash fingerprinting and a per-key skip index for idempotent, selective regeneration.",
    "maturity": "stable",
    "domains": [
        {"meta": "developer-tooling",
            "sub": "build-tooling"},
        {"meta": "data",
            "sub": "caching"}
    ],
    "capabilities": [
        "content-hash-fingerprint",
        "deterministic-file-set-hash",
        "per-key-skip-index",
        "regeneration-guard"
    ],
    "overlaps": [],
    "incompatibleWith": [],
    "supersedes": [],
    "governedBy": [
        "type-safety",
        "separation-of-concerns",
        "immutability"
    ],
    "visibility": {"private": false,
        "hidden": false},
    "ecosystem": "typescript",
    "docs": {
        "overview": "A dependency-free leaf that answers one question deterministically: have a generator's inputs changed since it last ran? It content-hashes a set of files (SHA-256 of bytes, order-independent), folds those hashes into a composite fingerprint, and persists a per-key index so a generator can skip the units whose inputs are unchanged and regenerate only those that moved.",
        "whenToUse": [
            "A code or doc generator that should skip regenerating an output whose precise inputs have not changed since the last run.",
            "Per-unit selective regeneration: hash each unit's own inputs plus a shared-input hash, so a shared change invalidates every unit while a single-unit change invalidates only that unit.",
            "Any build step wanting a deterministic, content-based (not mtime-based) up-to-date check with an ephemeral on-disk index."
        ],
        "whenNotToUse": [
            "Cryptographic integrity or tamper-evidence. The package is a change-detection fingerprint, not a security primitive.",
            "Detecting change in a live, in-memory object graph. The package hashes files on disk, so an in-memory hash cache fits better.",
            "A hybrid generated-and-authored output whose file must never be overwritten. The index says what changed, and preserving authored content stays with the caller."
        ],
        "quickStart": [
            {
                "intent": "Skip a unit whose inputs are unchanged",
                "lang": "js",
                "code": "import { collectFiles, fingerprint, fingerprintOf, createFingerprintIndex, cacheFile } from \"@govlab/content-fingerprint\";\nimport { existsSync } from \"node:fs\";\n\nconst index = createFingerprintIndex({ file: cacheFile(\"module-docs\"), force: process.env.GOVLAB_NO_CACHE === \"1\" });\nconst shared = fingerprint([canonicalIndexPath, allRulesPath, govlabConfigPath]);\nfor (const unit of units) {\n    const own = fingerprint([...collectFiles(unit.dir, { include: (n) => n.endsWith(\".ts\") }), unit.manifest]);\n    const key = fingerprintOf([own, shared, GENERATOR_SOURCE]);\n    if (index.unchanged(unit.id, key) && existsSync(unit.output)) { continue; }\n    render(unit);\n    index.update(unit.id, key);\n}\nindex.flush();"
            }
        ],
        "configuration": "No constructor options beyond the index file path and a `force` flag. Scalar knobs (hash algorithm, separators, index indent, default ignored directories, cache path segments) are package constants. The caller injects the cache file location through `cacheFile(name)`, which resolves the index under the consumer's `node_modules/.cache` (a govlab/fingerprint subfolder created on first write).",
        "disposal": [
            "Remove `govlab.root/govlab.utils/content-fingerprint/`.",
            "Drop `\"@govlab/content-fingerprint\": \"*\"` from the `govlab.quality`, `govlab.patterns`, and `govlab.docs` package manifests.",
            "Remove every `import … from \"@govlab/content-fingerprint\"` and inline or drop the skip check where still needed."
        ],
        "aiContext": [
            "The fingerprint is content-based (SHA-256 of file bytes), never mtime-based, so it is deterministic across machines and reruns.",
            "`fingerprint(files)` is order-independent (it sorts), while `fingerprintOf(parts)` is order-sensitive. The latter composes an own-hash, a shared-hash and the generator's own source hash into one key.",
            "The index lives under `node_modules/.cache` and is ephemeral: a fresh checkout has no index, so every unit regenerates and the result is authoritative.",
            "A correct per-unit key folds in every shared input (a change there must invalidate all units) and the generator's own source (a generator change must invalidate its outputs).",
            "A pure leaf: zero `@govlab/*` sibling dependencies."
        ],
        "apiNotes": [
            {
                "name": "hashFile",
                "note": "SHA-256 hex of a file's bytes, or the `absent` sentinel if the file does not exist. Any other read failure throws."
            },
            {
                "name": "fingerprint",
                "note": "the order-independent composite hash of a file set (path and content per file). A missing file hashes to the sentinel."
            },
            {
                "name": "fingerprintOf",
                "note": "the order-sensitive composite of already-computed hash strings, which folds the own, shared and generator-source hashes into one key."
            },
            {
                "name": "digestOf",
                "note": "SHA-256 hex of one string's exact bytes, with no separator added, so a reader can recompute it from the served body."
            },
            {
                "name": "collectFiles",
                "note": "deterministic sorted file list under a root, skipping the directories the caller names, with an optional name filter. An unreadable root yields an empty list."
            },
            {
                "name": "createFingerprintIndex",
                "note": "opens a per-key on-disk index exposing `unchanged`, `update` and `flush`, where `force` makes every key report changed."
            },
            {
                "name": "cacheFile",
                "note": "resolves an ephemeral index path under the consumer's node_modules/.cache/govlab/fingerprint/."
            }
        ]
    }
}
```